A valve timing control apparatus is used in an internal combustion engine such as an engine for an automobile. The apparatus adjusts valve opening/closing timings for rendering the internal combustion engine into a favorable operational condition, by varying the relative rotational phase between a driving-side rotary member rotated in synchronism with a crankshaft and a driven-side rotary member disposed coaxial with the driving-side rotary member and rotated in synchronism with a camshaft.
A valve timing control apparatus disclosed in PTL 1 is provided with a spring member configured to urge the relative rotational phase to the angle advancing direction. More particularly, this spring member provides the urging to the angle advancing direction in order to offset a force acting to the angle retarding direction that occurs in association with a torque variation of a cam mounted on the camshaft.
On the other hand, with the valve timing control apparatuses disclosed in PTL 1 and PTL 2, aluminum is employed as the material for forming the driving-side rotary member and the driven-side rotary member instead of the conventionally employed cast-iron type material or the like. In general, as aluminum is light-weight compared with the cast-iron type material, aluminum is suitable for use in an automobile for which weight reduction is sought for.